Study On Functional Properties Of Native Water-hyacinth Leaf Protein

The main target of this study was to evaluate functional properties of native water-hyacinth leaf protein (NWLP). Firstly, the native protein concentrate was prepared from water-hyacinth leaf by ethanol wash at low temperature. Then, water-hyacinth protein isolates preparation art, i.e., alkaline extraction followed by acid precipitation was optimized. Further studies were conducted to investigate the functional properties of NWLP.Using the protein extraction rate at various pHs as an indicator, experimental results showed that the best pH for the extraction of proteins would be 12. The orthogonal experiment was also undertaken to study on the effect of extraction temperature, NaCl concentration and time on protein extraction and precipitation rates. It was found that the most appropriate conditions for the preparation of water-hyacinth protein isolate using alkali extraction followed by acid precipitation would be pH12, temperature 60℃, time 30min, 0.4mol/L NaCl, solid/liquid 1:25 for extraction and the best pH for the precipitation of proteins was 5.5. At pH 5.5, 72.15% proteins were precipitated. Under the optimal conditions, protein extraction rate and protein content of the product were 65.87% and 91.2%, respectively.Using PDI as an indicator, study on the effect of pH, temperature and ionic strength on the dispersibility of NWLP was carried out. The dispersibility of NWLP varied with changing in temperature, pH and ionic strength. The PDI was the lowest at pH 5.5. It was the highest at 60℃compared to those of other temperatures, which was 60%. The PDI of water-hyacinth leaf proteins increased dramatically as the ionic strength was increased from 0.05 to 0.3 mol/L, and then become relatively stable. The PDI of water-hyacinth leaf proteins gradually decreased, as the NaCl concentration was more than 0.4 mol/L.Experimental results showed that the emulsifying capacity of water hyacinth leaf protein increased as the amount of proteins added was increased and that the emulsion stability is quite good. In the range of 0.4-1mol/L sodium chloride concentrations, the emulsifying capacity of water hyacinth leaf protein decreased as the sodium chloride concentration was increased, and the emulsion stability was not quite changed. The emulsifying capacity of water hyacinth leaf protein was good at pH 8-12, but the best stable emulsion among all pHs studied was prepared at pH 5.5.The experimental results also showed that the foaming capacity of water hyacinth leaf protein increased as protein concentration increased from 0.5% to 2% and it reached the maximal value at 2% protein concentration. Although the total volume of foaming increased, the foaming capacity of water hyacinth leaf protein decreased as protein concentration continued to increase. The foaming capacity of the water hyacinth leaf protein increased as NaCl concentration increased from 0.2-0.6mol/L. It reached the maximal value at 0.6mol/L NaCl concentration and its stability was the highest among all tests. It and its stability decreased slowly with the further increase of NaCl concentration. It and its stability were the lowest at pH 5.5 among all pHs tested.It was not able to form protein fiber at pH value below 10 or after stirring for less than 30min or at the water hyacinth leaf protein concentration lower than 10%. The pure water hyacinth leaf protein fiber prepared was crispy, un-springy, and easy to be broken.The proteinase activity in water hyacinth leaves is 1060U/g. This finding may be applicable for the extraction of proteins and the production of different hydrolyzed proteins from water hyacinth leaves.